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Subject[PATCH 1/3] mm, page_owner: fix off-by-one error in __set_page_owner_handle()
Date
As noted by Kirill, commit 7e2f2a0cd17c ("mm, page_owner: record page owner for
each subpage") has introduced an off-by-one error in __set_page_owner_handle()
when looking up page_ext for subpages. As a result, the head page page_owner
info is set twice, while for the last tail page, it's not set at all.

Fix this and also make the code more efficient by advancing the page_ext
pointer we already have, instead of calling lookup_page_ext() for each subpage.
Since the full size of struct page_ext is not known at compile time, we can't
use a simple page_ext++ statement, so introduce a page_ext_next() inline
function for that.

Reported-by: Kirill A. Shutemov <kirill@shutemov.name>
Fixes: 7e2f2a0cd17c ("mm, page_owner: record page owner for each subpage")
Signed-off-by: Vlastimil Babka <vbabka@suse.cz>
---
include/linux/page_ext.h | 8 ++++++++
mm/page_ext.c | 23 +++++++++--------------
mm/page_owner.c | 15 +++++++--------
3 files changed, 24 insertions(+), 22 deletions(-)

diff --git a/include/linux/page_ext.h b/include/linux/page_ext.h
index 682fd465df06..5e856512bafb 100644
--- a/include/linux/page_ext.h
+++ b/include/linux/page_ext.h
@@ -36,6 +36,7 @@ struct page_ext {
unsigned long flags;
};

+extern unsigned long page_ext_size;
extern void pgdat_page_ext_init(struct pglist_data *pgdat);

#ifdef CONFIG_SPARSEMEM
@@ -52,6 +53,13 @@ static inline void page_ext_init(void)

struct page_ext *lookup_page_ext(const struct page *page);

+static inline struct page_ext *page_ext_next(struct page_ext *curr)
+{
+ void *next = curr;
+ next += page_ext_size;
+ return next;
+}
+
#else /* !CONFIG_PAGE_EXTENSION */
struct page_ext;

diff --git a/mm/page_ext.c b/mm/page_ext.c
index 5f5769c7db3b..4ade843ff588 100644
--- a/mm/page_ext.c
+++ b/mm/page_ext.c
@@ -67,8 +67,9 @@ static struct page_ext_operations *page_ext_ops[] = {
#endif
};

+unsigned long page_ext_size = sizeof(struct page_ext);
+
static unsigned long total_usage;
-static unsigned long extra_mem;

static bool __init invoke_need_callbacks(void)
{
@@ -78,9 +79,8 @@ static bool __init invoke_need_callbacks(void)

for (i = 0; i < entries; i++) {
if (page_ext_ops[i]->need && page_ext_ops[i]->need()) {
- page_ext_ops[i]->offset = sizeof(struct page_ext) +
- extra_mem;
- extra_mem += page_ext_ops[i]->size;
+ page_ext_ops[i]->offset = page_ext_size;
+ page_ext_size += page_ext_ops[i]->size;
need = true;
}
}
@@ -99,14 +99,9 @@ static void __init invoke_init_callbacks(void)
}
}

-static unsigned long get_entry_size(void)
-{
- return sizeof(struct page_ext) + extra_mem;
-}
-
static inline struct page_ext *get_entry(void *base, unsigned long index)
{
- return base + get_entry_size() * index;
+ return base + page_ext_size * index;
}

#if !defined(CONFIG_SPARSEMEM)
@@ -156,7 +151,7 @@ static int __init alloc_node_page_ext(int nid)
!IS_ALIGNED(node_end_pfn(nid), MAX_ORDER_NR_PAGES))
nr_pages += MAX_ORDER_NR_PAGES;

- table_size = get_entry_size() * nr_pages;
+ table_size = page_ext_size * nr_pages;

base = memblock_alloc_try_nid(
table_size, PAGE_SIZE, __pa(MAX_DMA_ADDRESS),
@@ -234,7 +229,7 @@ static int __meminit init_section_page_ext(unsigned long pfn, int nid)
if (section->page_ext)
return 0;

- table_size = get_entry_size() * PAGES_PER_SECTION;
+ table_size = page_ext_size * PAGES_PER_SECTION;
base = alloc_page_ext(table_size, nid);

/*
@@ -254,7 +249,7 @@ static int __meminit init_section_page_ext(unsigned long pfn, int nid)
* we need to apply a mask.
*/
pfn &= PAGE_SECTION_MASK;
- section->page_ext = (void *)base - get_entry_size() * pfn;
+ section->page_ext = (void *)base - page_ext_size * pfn;
total_usage += table_size;
return 0;
}
@@ -267,7 +262,7 @@ static void free_page_ext(void *addr)
struct page *page = virt_to_page(addr);
size_t table_size;

- table_size = get_entry_size() * PAGES_PER_SECTION;
+ table_size = page_ext_size * PAGES_PER_SECTION;

BUG_ON(PageReserved(page));
kmemleak_free(addr);
diff --git a/mm/page_owner.c b/mm/page_owner.c
index dee931184788..d3cf5d336ccf 100644
--- a/mm/page_owner.c
+++ b/mm/page_owner.c
@@ -156,10 +156,10 @@ void __reset_page_owner(struct page *page, unsigned int order)
handle = save_stack(GFP_NOWAIT | __GFP_NOWARN);
#endif

+ page_ext = lookup_page_ext(page);
+ if (unlikely(!page_ext))
+ return;
for (i = 0; i < (1 << order); i++) {
- page_ext = lookup_page_ext(page + i);
- if (unlikely(!page_ext))
- continue;
__clear_bit(PAGE_EXT_OWNER_ACTIVE, &page_ext->flags);
#ifdef CONFIG_DEBUG_PAGEALLOC
if (debug_pagealloc_enabled()) {
@@ -167,6 +167,7 @@ void __reset_page_owner(struct page *page, unsigned int order)
page_owner->free_handle = handle;
}
#endif
+ page_ext = page_ext_next(page_ext);
}
}

@@ -186,7 +187,7 @@ static inline void __set_page_owner_handle(struct page *page,
__set_bit(PAGE_EXT_OWNER, &page_ext->flags);
__set_bit(PAGE_EXT_OWNER_ACTIVE, &page_ext->flags);

- page_ext = lookup_page_ext(page + i);
+ page_ext = page_ext_next(page_ext);
}
}

@@ -224,12 +225,10 @@ void __split_page_owner(struct page *page, unsigned int order)
if (unlikely(!page_ext))
return;

- page_owner = get_page_owner(page_ext);
- page_owner->order = 0;
- for (i = 1; i < (1 << order); i++) {
- page_ext = lookup_page_ext(page + i);
+ for (i = 0; i < (1 << order); i++) {
page_owner = get_page_owner(page_ext);
page_owner->order = 0;
+ page_ext = page_ext_next(page_ext);
}
}

--
2.23.0
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